Computer system and method for sharing computer memory

ABSTRACT

A computer system has a plurality of computer servers, each including at least one central processing unit (CPU). A memory appliance is spaced remotely from the plurality of computer servers. The memory appliance includes random access memory (RAM). A photonic CPU link is operatively attached to the at least one CPU. A photonic circuit switch is operatively attached to the photonic CPU link. An allocated portion of the RAM is addressable by a predetermined CPU selected from the plurality of computer servers.

BACKGROUND

The present disclosure relates generally to connection of memoryappliances for computer systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the present disclosure willbecome apparent by reference to the following detailed description anddrawings, in which like reference numerals correspond to similar, thoughperhaps not identical, components. For the sake of brevity, referencenumerals or features having a previously described function may or maynot be described in connection with other drawings in which they appear.

FIG. 1 is a schematic representation of a computer system according toan embodiment of the present disclosure;

FIG. 2 is a schematic representation of embodiments of additionalaspects of the embodiment of the computer system shown in FIG. 1;

FIG. 3 is a schematic representation of another embodiment of a computersystem according to the present disclosure;

FIG. 4 is a schematic representation of an embodiment of a memoryappliance according to an embodiment of the present disclosure;

FIG. 5 is a schematic representation of an embodiment of a link-attachedmemory domain according to an embodiment of the present disclosure;

FIG. 6 is a schematic representation of an embodiment of acommunications path from CPU to RAM according to an embodiment of thedisclosure;

FIG. 7 is a schematic process flow diagram of embodiments of the methodof the present disclosure;

FIG. 8 is a schematic representation of a photonic circuit switchaccording to an embodiment of the present disclosure;

FIG. 9 is a schematic representation of an embodiment of a photoniccircuit switch connecting severs and memory according to an embodimentof the present disclosure;

FIG. 10 is a high-level functional block schematic of an embodiment ofan integrated circuit chip according to an embodiment of the presentdisclosure;

FIG. 11 is a schematic representation of an embodiment of a photoniccircuit switch configuration for the embodiment shown in FIG. 9;

FIG. 12 is a schematic diagram showing an embodiment of photonic circuitswitch settings for the embodiment of the photonic circuit switchconfiguration shown in FIG. 11;

FIG. 13 is a schematic representation of an embodiment of photoniccircuit switch configuration for the embodiment shown in FIG. 9;

FIG. 14 is a schematic diagram showing an embodiment of photonic circuitswitch settings for the embodiment of the photonic circuit switchconfiguration shown in FIG. 13;

FIG. 15 is schematic representation of an embodiment of a photoniccircuit switch, configuration for the embodiment shown in FIG. 9; and

FIG. 16 is a schematic diagram showing an embodiment of photo is circuitswitch settings for the embodiment of the photonic circuit switchconfiguration shown in FIG. 15.

DETAILED DESCRIPTION

A typical central processing unit (CPU) in a computer system maylogically address many times the number of memory locations than it canphysically control. For example, many CPUs can logically address between2 TB (2000 GB) and 4 TB (4000 GB) of memory, but can only physicallycontrol 12 GB. The fundamental constraints on the number of memorylocations are the input/output (I/O) pin count and the power required todirectly sustain multiple Double Data Rate (DDR) busses from a singleCPU, State-of-the-art CPUs limit their glueless (not using a secondaryswitching/coherency connectivity hierarchy) connectivity to a domain of8 processors, and each processor can only control an extreme subset ofwhat it can address. Thus, using processors as Memory controllers may bea relatively expensive means for both addressing and controlling a largeamount of memory.

Symmetric MultiProcessing (SMP) is a computer system architecture inwhich a plurality of CPUs shares the same memory. SMP systems providescalability. As business increases, additional CPUs can be added toabsorb the increased transaction volume. The number of CPUs in SMPsystems may range from at least two to more than 32 CPUs.

SMP architectures allow large amounts of memory to be addressed by eachCPU by coming many CPUs with a proprietary switching fabric employing aconsistent memory coherency scheme over the entire complex. Thissolution is 1) relatively complex, 2) expensive, 3) adds significantlatency, and 4) is not suited to certain applications, includingsearching.

DDR expansion schemes have also been used to increase memory availableto CPUs. An example of a DDR expansion scheme includes Load Reduced Dualin-line Memory Modules (LRDIMMs), LRDIMMs may increase overall serversystem memory capacity and speed using a memory buffer chip or chips asopposed to a register. The LRDIMM solutions typically increase thecontrollable amount of memory by single-digit factors, while creatinghigh-power custom DIMMs that may be expensive relative to the valueprovided.

Another DDR expansion scheme includes chipsets that expand the amount ofmemory that can be controlled by an existing memory controller. Thechipset solutions stretch DDR timing to limits, add power, and do notprovide extreme levels of scaling in terms of memory radius. As usedherein, the term “memory radius” means an amount of memory that can beattached to a particular entity. Scaling using the chipset solution islimited by the amount of memory that can be packaged with a requiredproximity to the memory controller.

A drawback of the DDR expansion schemes outlined above is that theycannot be configured for one ratio, and then changed to another ratio ata subsequent configuration event.

Another solution for memory expansion is to build a mainframe computer.Mainframe computers run multiple uses and multiple jobs, and canallocate memory based upon needs. A drawback of mainframe computers isthat they are generally expensive, and the total size of the memoryexpansion is limited.

I/O connected memory may be used as a memory expansion technique. I/Oconnected memory is expansion memory that connects to servers issoftware calls to I/O. However, high latency associated with softwarecalls to I/O generally limits the value of I/O connected memory as asolution for memory expansion.

A link-based memory expansion approach uses CPU links to electronicallyor photonically connect a server to remote memory. However, theconnection is point-to-point; thus the link-based memory expansionconnects one processor to one memory unit. Link-based memory expansiondoes not address flexibly sharing a pool of memory resources betweenmultiple servers.

A link-based memory expansion with an electronic packet switch approachovercomes the limitations of the point-to-point network by adding anelectronic packet switch. However, a packet switch typically adds tensof nanoseconds of latency and consumes significant power. The high-speedlink must be slowed and re-clocked to match the core frequency of theswitch, routed, then re-clocked to the high-speed output path. Ahierarchy of these switches adds hundreds of nanoseconds of latency, assequential hops penalize performance.

A computer system with a photonically-attached memory expansionappliance is disclosed herein. Embodiments of the computer systemprovide the ability to change which memory domains are available towhich servers at a configuration event. The system uses a native CPUlink to a remote node, and allows adding nodes within the limits of theCPU architecture. The memory that can be attached per node is notfundamentally constrained as described above with memory attached toCPUs, since the CPU links can be allocated to serve many more memorybusses per node than per processor. Thus, large amounts of memory may beallocated to a memory intensive process on a CPU for an application (forexample, searching a large database), while an application that requirestoss memory will have an appropriate amount allocated to it on an otherCPU (for example, word processing). On a different occasion, differentamounts of memory may be allocated to the CPU and the other CPU.Reconfiguring the memory allocated to a CPU from a pool of memory may bean efficient use of memory.

In contrast, other computer systems may permanently allocate a largeamount of memory to each CPU to provide capability to perform memoryintensive operations when required, but much of the memory would beunder-used during operations that do not require much memory. Costsassociated with procurement of the additional memory and powerconsumption incurred by unused memory are inefficiencies that may beovercome with embodiments of the present disclosure.

Embodiments of the computer system of the present disclosure enable theuse of relatively inexpensive, industry-standard servers. Theconfigurable memory resource pool can be allocated to meet customer andapplication needs. The disclosed computer system may be particularlyuseful for search applications and cloud architectures.

Referring now to FIG. 1, an embodiment of a computer system 100 isdepicted. The computer system includes a server rack 140 and a memoryrack 145 having a photonic interconnection 150 therebetween. The serverrack 140 includes a plurality of computer servers 105 operativelydisposed in the server rack 140. The memory rack 145 includes one ormore memory appliances 130. Although FIG. 1 depicts a multi-rackembodiment of the present disclosure, it is to be understood that thememory appliance 130 and computer servers 105 may be housed within thesame rack (not shown).

FIG. 2 shows further aspects of the embodiment of the computer system100 depicted in FIG. 1. Each computer server 105 includes at least onecentral processing unit (CPU) 110 operatively disposed therein. A memoryappliance 130 is spaced remotely from the plurality of computer servers105 and includes a photonic circuit switch 155, and a link attachedmemory domain 180 operatively disposed therein. It is to be understoodthat a photonic circuit switch 155 may also be known as a photonicfall-through switch. The ink attached memory domain 180 includes memorycontroller 160, random access memory (RAM) 170 and an integrated circuitchip 182 that is configured to function as a memory controller 160 andas a CPU-link-to-DDR communications chip 162 operatively disposed in thememory appliance 130. At least one photonic interconnection 150 connectsthe plurality of computer servers 105 and the memory appliance 130. Aconverter 135 may be operatively disposed between the CPU and thephotonic interconnection 150 to facilitate bidirectional communicationbetween the CPU 105 that communicates electronically, and the photonicinterconnection 150. Further, although FIG. 2 does not show thisconfiguration, it is to be understood that two or more photonicinterconnections 150 may connect each CPU 110 to the memory appliance130 for bandwidth, redundancy, and latency considerations.

In an embodiment, an allocated portion of the RAM 170 is addressable bya predetermined CPU 110 selected from the plurality of CPUs 110 disposedin the plurality of computer servers 105 during a configuration event.The selected CPU 110 may be selected based on many factors, e.g., theprograms that need to be executed in the computer, database size, thesize of the calculation task, etc. For example, a CPU 110 may beallocated a large portion of RAM 170 to search large databases. Inanother example, a maximum allocated portion of the RAM 170 addressableby the predetermined CPU 110 is about 100 percent of the RAM 170operatively disposed in the memory appliance. In yet another example, aratio of a maximum allocated portion of the RAM 170 to CPU cores 112 isat least about 64 GB/core in the predetermined CPU 110.

In a further example, 90 percent of the RAM 170 may be allocated to thepredetermined CPU 110, and all of the remaining CPUs 110 combined may beallocated a remaining 10 percent of the RAM 170 until a subsequentconfiguration event. At the subsequent configuration event, analternative predetermined CPU 110 may be allocated 30 percent of the RAM170 operatively disposed in the memory appliance, while the remainder ofthe CPUs 110 is allocated 70 percent of the RAM 170 in the aggregate.

It is to be understood that all of the CPUs 110 have some level ofnative memory. As used herein, portions of the RAM 170 allocated duringconfiguration events are disposed in the memory appliance 130 separatefrom, and in addition to the native CPU memory.

The allocated portion of the RAM 170 is established and maintainedthroughout operations of the computer system 100 until a subsequentconfiguration event. It is to be understood that establishing anallocated portion of RAM 170 means that a particular range (not shown)of memory locations in the RAM 170 are) designated for the exclusive useof a particular CPU 110, and the exclusive allocation does not change,(i.e., is maintained throughout operations) until a subsequentconfiguration event.

A configuration event may be a boot operation, or similar eventdetermined by the operating system, by hypervisior appliance firmware,or by other control means. Configuration events may also include, butare not limited to instantiation of virtual machines, periodicreconfiguration of the computer system 100 (e.g., for business needs ona monthly, quarterly, yearly, etc. basis), and the like, andcombinations thereof.

It is to be understood that, in embodiments of the present disclosure,memory may be assigned to a CPU during any configuration events of thecomputer system 100, and such assignment is not limited to during a bootor similar configuration event.

It is to be further understood that “configuration events” as usedherein generally speaks to time granularity. By way of example, ifmemory could be allocated on a per-instruction basis, then aconfiguration mechanism would react within the time expectations for aninstruction in the computer system (e.g., nanoseconds). Alternatively,if memory were to be allocated on a per-Virtual-machine instance basis,then the configuration mechanism reacts within the time of aVirtual-machine instance (e.g., microseconds to milliseconds).Configuration events contemplated as being within the purview of thepresent disclosure are associated with configuration mechanisms (e.g.,circuit switches 155 as disclosed herein and the electronic controlthereof (see reference numeral 151 in FIG. 8)) that are not as fast asthe per-instruction example, but are as fast or faster than theper-Virtual-machine instance example. In an embodiment, a configurationevent is executed by a configuration mechanism in about 100 millisecondsor less. In an alternate embodiment, the event execution time rangesfrom about 50 microseconds to about 100 milliseconds. In otherembodiments, the event execution time may be less than 50 microseconds.

As also shown in FIG. 2, the RAM 170 may be in the form of DIMMs 122,which may be organized in a manner related to specific DDR busses. It isto be understood that other forms of RAM 170 may also be used, includingbut not limited to memory platters, memory cards, stacked DRAM packages,phase-change memory, and memristor-based memory.

Referring now to FIG. 3, an embodiment of a computer system 100′ has aplurality of computer servers 105 operatively connected to a memoryappliance. 130 via photonic interconnections 150. In the embodimentdepicted in FIG. 3, the computer servers 105′ are dual-socket servers.It is to be understood that a dual-socket server includes two CPUs 110(CPUs not shown in FIG. 3 for clarity). It is to be further understoodthat other embodiments of the computer server may include more CPUs 110than described above, and other embodiments of the computer system mayinclude more computer servers 105, 105′ than shown. For example, in anembodiment, each of the plurality of servers may include more than eightCPUs. In a non-limiting example, a computer system 100, 100′ may include1024 CPUs.

FIG. 4 depicts the photonic interconnections 150 connecting CPU links152 to the memory appliance 130. A photonic circuit switch 155 connectsthe CPU links 152 to link-attached memory domains 180. A converter 135is operatively disposed between the photonic circuit switch 155 and thelink-attached memory domains 180. The converter 135 converts the CPUlink signal from a photonic CPU link signal to an electronic CPU linksignal. It is to be understood that the converter 135 is bidirectional,therefore converter 135 converts photonic to electronic signals andelectronic to photonic signals.

FIG. 5 shows an individual link attached memory domain 180 including anintegrated circuit (IC) chip 182. IC chip 182 is configured to functionas a memory controller 160 and as a CPU-link-to-DDR communications chip162 (as shown in FIG. 2). The DIMMs 122 communicate via a DDR bus 184thereby completing the path between the CPU 110 and RAM 170 (as seen inFIGS. 2, 4 and 5 together).

FIG. 8 schematically depicts photonic circuit switch 155 according to anembodiment of the present disclosure. (It is noted that FIG. 6 and FIG.7 will be discussed hereinbelow.) As also shown in FIG. 4, photoniccircuit switch 155 switches photonic interconnections 150 to connect CPUlinks 152 with link-attached memory domains 180. As shown in FIG. 8, thephotonic circuit switch 155 is electronically controlled, asschematically depicted at reference numeral 151. As such, electroniccontrols may be changed during configuration events, resulting inchanges in connectivity between specific photonic inputs and specificphotonic outputs of the photonic circuit switch 155.

Attributes of photonic circuit switches 155 include relatively slow timeto switch (typically hundreds of microseconds to tens of milliseconds),but once switched, they have a very short propagation delay time(generally hundreds of picoseconds). In the embodiments herein, thephotonic circuit switch 155 switches infrequently relative to the rateof data passing through the switch (when the memory configuration ischanged), but once switched, the photonic circuit switch 155 providesvery low-latency and high bandwidth communications. In embodiments ofthe present disclosure, the photonic circuit switch 155 may beconfigured to have a switch time from about 50 microseconds to about 100milliseconds. In other embodiments, the switch time may be less than 50microseconds.

As mentioned above, it is to be understood that memory allocation andreallocation need not be restricted to a boot or similar configurationevent, as discussed above. In embodiments of the present disclosure,memory load shifting may be accomplished as a function of changingapplication demand.

It is to be understood that photonic circuit switch 155 may beprovisioned as a MicroElectroMechanical Systems (MEMS) switch, whichUses steeling mirrors to change optical signal connectivity. Thephotonic circuit switch 155 may also be provisioned as a Liquid CrystalDisplay (LCD) switch, which uses a power splitter along with an LCDarray to block the non-desired optical path. Additionally, Mach-ZehnderInterferometer (MZI) switches, ring modulator switches, and othersilicon photonic techniques which provide the ability to selectivelyroute signals may be used. A non-limiting example of a photonic circuitswitch 155 may be found in the “intelligent Optical System 100” fromGlimmerglass Networks in Hayward, Calif.

It is to be further understood that a photonic circuit switch 155 mayinclude an array or network of photonic circuit switches 155. Forexample, as used herein, photonic circuit switch 155 may include alinear array of photonic circuit switches. In yet another example, aphotonic circuit switch 155 may include a cascade of photonic circuitswitches.

FIG. 6 shows a schematic view of a communications path from a CPU 110 toRAM 170 in an embodiment of the present disclosure. All the CPU is 110include at least one CPU core 112 (shown schematically in FIG. 6). CPU110 is connected via fanout 171 on a local bus 173 to memory modules 175within local memory 172. A CPU link 152 is connected to a converter 135that converts an electronic CPU link signal to a photonic. CPU linksignal that is carried by a photonic interconnection 150 to anotherconverter 135 that converts the CPU link signal from a photonic CPU linksignal to an electronic CPU link signal. It is to be understood that asused herein, a photonic interconnection 150 may include more than oneoptical path. For example, more than one optical fiber (not shown) maybe included in photonic interconnection 150. It is to be furtherunderstood that the communication across the photonic interconnection150 may be bidirectional (i.e., one optical fiber communicates in onedirection, and another optical fiber communicates in an oppositedirection), therefore the converters 135 convert photonic to electronicsignals and electronic to photonic signals. CPU-link-to-DDRcommunications chip 162 connects the CPU links 152 to RAM 170 via DDRbus 164. It is to be understood that the photonic interconnection 150may include a light transmitting (optical) fiber, couplings (not shown),an converters 135.

Photonic interconnection 150 allows RAM 170 to be located at a greaterdistance from the CPU 110 (compared to electronic interconnection)without high transport delay times associated with multiple-chip hopsand with excellent signal to noise properties. It is to be understoodthat the product of the speed of light and the length of the fibercontinues to be a source of transport delay, but not a significanttransport delay at the communication radius disclosed herein. Thus, anembodiment of the disclosure may have a communication radius rangingfrom about 1 meter to about 10 meters. As shown in FIG. 1, thiscommunication radius allows the memory appliance(s) 130 to be disposedin a memory rack 145 spaced apart from a server rack 140 withoutperformance issues related to transport time until the length of thefiber is such that the product of the speed of light and the length ofthe fiber becomes a significant part of the delay. The communicationradius disclosed in the present disclosure may be one or two orders ofmagnitude greater than a DDR2 or DDR3 communication radius.

In the embodiment depicted in FIG. 9, an example system implementationconnects 8 servers 105 each having two CPU links 152 to a photoniccircuit switch 155 serving 8 link-attached memory domains 180. As alsodepicted in FIG. 4, converters 135 are operatively disposed between thephotonic circuit switch 155 and the link-attached memory domains 180.The converters 135 convert the CPU link signals from photonic CPU linksignals to electronic CPU link signals. It is to be understood that theconverters 135 convert photonic to electronic signals and electronic tophotonic signals. It is to be further understood that converters 135shown on the left side of the photonic circuit switch 155 in FIG. 9facilitate bidirectional communication between the CPU links 152 thatcommunicate electronically; and photonic circuit switch 155 thatcommunicates photonically.

In FIG. 9, each server 105 has a label S0, S1, . . . S7. Each server 105has two CPU links 152 labeled L0, and L1. Thus, reference to aparticular CPU link 152 of the 16 CPU links 152 shown in GIG. 9 may beaccomplished by calling out the server label and the link label (e.g.S0L0, S0L1, S1L0 . . . S7L1). In an explanatory example, the CPU link152 with the label S1L1 indicates that the respective CPU link 152 isattached to Server 1, Link 1. Each CPU link 152 is a full bi-directionalCPU link. It is to be understood that a bi-directional CPU link has thefollowing characteristics: all server outputs are routed to switchinputs, all server inputs are routed to switch outputs, all memorydomain inputs are routed to switch outputs, and all memory domainoutputs are routed to switch inputs, in the embodiment shown in FIG. 9,each of the 8 servers 105 has access to a maximum of 4 link attachedmemory domains 180, however, it is not necessary for a server to beattached to any of the memory domains 180.

FIG. 10 shows a high-level functional block schematic of the integratedcircuit chip 182 also shown in FIG. 2. The basic, functionality of theintegrated circuit chip 182 includes link control, link bridging, memorycontrol, and DDR physical control functions.

Various configurations of attached memory are shown in FIGS. 11-16. FIG.11 shows a particular switch configuration of the embodiment shown inFIG. 9. In FIG. 11, the CPU links 152 and link-attached memory domainlinks 153 are mapped in 1:1 correspondence. This configuration providesthe highest bandwidth available.

FIG. 12 is a schematic diagram showing exemplary switch settings for theswitch configuration shown in FIG. 11. It is to be understood that forsimplicity, not all inputs and outputs are shown. For example, the inputA0 represents the inputs required for an entire full-width CPU link. Asshown in the switch map block, the CPU links 152 and the link-attachedmemory domain links 153 are mapped in 1:1 correspondence. The links 152,153 are bi-directional.

FIG. 13 shows a moderate connectivity and bandwidth switch configurationof the embodiment shown in FIG. 9. In FIG. 13, two link-attached memorydomains 180 are connected to each server 105. This configurationprovides medium bandwidth and medium memory radius.

FIG. 14 is a schematic diagram showing exemplary switch settings for theswitch configuration shown in FIG. 13. Again, it is to be understoodthat for simplicity, not all inputs and outputs are shown. For example,the input A0 represents the inputs required for an entire full-width CPUlink. As shown in the switch map block, certain link-attached memorydomain links 153 are unused. In FIG. 14, dashed lines indicate linksthat are not connected. Photonic circuit switch 155 output Y2 and inputA3 are shown as not connected (NC) in the Switch Map portion of FIG. 14.Links 152, 153 are bi-directional.

FIG. 15 shows a large connectivity and lower bandwidth switchconfiguration of the embodiment shown in FIG. 9. In FIG. 15, fourlink-attached memory domains 180 are connected to each server 105. Thisconfiguration provides a high memory radius with a lower bandwidth ascompared to the configurations shown in FIGS. 11-14.

FIG. 16 is a schematic diagram showing exemplary switch settings for theswitch configuration shown in FIG. 15. Once again, it is to beunderstood that for simplicity, not all inputs and outputs are shown.Also for simplicity, only a single CPU link 152 is shown in FIG. 16. Asin FIGS. 12 and 14, the input A0 represents the inputs required for anentire full-width CPU link. As shown in the Switch Map block, certainlink-attached memory domain links 153 are connected to otherlink-attached memory domain links 153, thereby providing one CPU link152 access to two link-attached memory domains 180. Electronic circuitswitch 155 input A3 is connected to output Y4 and input A4 is connectedto output Y2 in the Switch Map portion FIG. 16. Also shown in FIG. 14,the links 152, 153 are bi-directional.

FIG. 7 depicts a method 200 for sharing computer memory in a computersystem having a plurality of Central Processing Units (CPUs). Anembodiment of the method 200 includes photonically connections thePlurality of CPUs to a memory appliance spaced remotely from theplurality of CPUs, the memory appliance having random access memory(RAM) operatively disposed there is, depicted at reference numeral 210.Method 200 further includes exclusively allocating, via a photoniccircuit switch, a portion of the RAM to a predetermined CPU selected theplurality of CPUs, as depicted at reference numeral 220.

The method 200 may further include establishing and maintaining theexclusive allocation of the RAM to the CPU during operations of thecomputer system until a subsequent configuration event, as depicted atreference numeral 230.

It is to be understood that as used herein, “spaced remotely” from theplurality of CPUs means the memory appliance(s) 130 are spaced apartfrom the plurality of CPUs, by a distance ranging from about 1 meter toabout 10 meters.

According to the embodiments herein, a total amount of RAM 170operatively disposed in the memory appliance 130 in Gigabytes divided bya total number of CPU cores 112 in the plurality of computer servers 105is at least about 64 GB/core (expressed another way, the memoryappliance 130 includes a quantity of random access memory (RAM) 170equal to the mathematical product of 64 GB and the total number of CPUcores 112 in the computer system 100). In another embodiment, the totalRAM to CPU core ratio is 256 GB/core, in yet another embodiment, thetotal RAM to CPU core ratio is 2000 GB/core. It is to be understood thatthe example total RAM to CPU core ratios above are not intended to implya uniform allocation of RAM 170 to all of the CPUs 110 in the servers105 in the computer system 100, although the CPUs 110 may be souniformly provisioned, if desired. In embodiments disclosed herein, theRAM 170 allocation may be skewed such that a large amount of memory (ofthe total RAM 170 available) is allocated to one or r core CPUs 110,with the remaining amount of memory (of the total RAM 170 available)being allocated as desired to the remaining CPUs 110.

Each of be plurality of computer servers in the embodiments herein maybe dual-socket servers. In another embodiment, the computer servers mayinclude between one and eight CPUs. It is to be understood that morethan one CPU may be operatively disposed on a single chip (i.e.,dual-core and quad-core processors).

It is to be further understood that embodiments of the presentdisclosure are not limited to the native capacity provided by a CPUmemory controller. For example, a CPU having four DDR busses with fourDIMMs each would have a maximum native capacity of 4×4×(DIMM capacity).If the DIMM capacity were 8 GB, the maximum native capacity would be4×4×8=128 GB. Carrying forward with the same example, if the CPU has 8cores 112, the memory per core would be 128 GB/8=16 GB. If the CPU inthe example were part of an 8-way SMP, the maximum memory would be 1024GB but the RAM to CPU core ratio would still be 16 GB/core.

In another example of memory limited by the native capacity of the CPUmemory controller, a Beckton CPU having 8 cores can control 16 DIMMs. Ifthe DIMMs are 8 GB DIMMs, then the ratio of RAM to CPU cores is 16GB/core.

In contrast, embodiments of the present disclosure could make all of theRAM 170 available to a single server 105. As such, if the memoryappliance 130 supports 128 DIMMs 122, then the total RAM/CPU core ratiois (128 DIMMs×8 GB/DIMM)/(8 cores/CPU×2 CPUs)=64 GB/core, it is to beunderstood that if the memory appliance 130 supports more DIMMs 122, theratio of RAM to CPU cores will be greater.

Further, as mentioned above, in embodiments of the present disclosure, amaximum allocated portion of the RAM addressable by the predeterminedCPU is about 100 percent of the RAM operatively disposed in the memoryappliance(s) 130. It is to be understood that if the predetermined CPU110 is allocated 100 percent of the RAM 170 from the memory appliance(e)130, the remaining CPUs 110 will receive no additional memory from thememory appliance(s) 130 until a subsequent reallocation at a subsequentconfiguration event.

The RAM 170 may be double data rate (DDR) RAM. Other forms of RAM arealso contemplated as being within the purview of the present disclosure,including but not limited to memory platters, memory cards, stacked DRAMpackages, phase-change memory, and memristor-based memory.

It is to be understood that the terms “attached/attaches/attaching to”and “Connected/connects/connecting to” are broadly defined herein toencompass a variety of divergent connected arrangements and assemblytechniques. These arrangements and techniques include, but are notlimited to (1) the direct communication between one component andanother component with no intervening components therebetween; and (2)the communication of one component and another component with one ormore components therebetween, provided that the one component being“attached to” or “connected/ing to” the other component is somehow inoperative communication with the other component (notwithstanding thepresence of one or more additional components therebetween).

While several embodiments have been described in detail, it will beapparent to those skilled in the art that the disclosed embodiments maybe modified. Therefore, the foregoing description is to be considerednon-limiting.

What is claimed is:
 1. A computer system, comprising: a plurality ofcomputer servers, each including at least one central processing unit(CPU); a memory appliance spaced remotely from the plurality of computerservers and including link-attached memory domains with random accessmemory (RAM) therein, wherein the plurality of computer servers areoperatively connected to the link-attached memory domains of the memoryappliance via photonic connections; and a photonic circuit switchcontrolled by an electronic control during a configuration event tochange the photonic connections between the plurality of computerservers and the link-attached memory domains of the memory appliance andto allocate a portion of the RAM, during the configuration event, to apredetermined CPU in the plurality of computer servers based on databasesize that the predetermined CPU is to search.
 2. The computer system asdefined in claim 1, wherein the memory appliance is located at adistance ranging from 1 meter to 10 meters from the plurality ofcomputer servers.
 3. The computer system as defined in claim 1, whereinthe photonic circuit switch is to have a switch time less than 100milliseconds.
 4. The computer system as defined in claim 1, wherein thephotonic circuit switch is to have a propagation delay time of between50 picoseconds and 500 picoseconds.
 5. The computer system as defined inclaim 1, wherein the photonic circuit switch is selected from a groupconsisting of MicroElectroMechanical Systems (MEMs) switches, LiquidCrystal Display (LCD) switches, Mach-Zehnder Interferometer (MZI)switches, ring modulator switches, and combinations thereof.
 6. Thecomputer system as defined in claim 1, wherein the photonic circuitswitch is an LCD switch, and wherein the LCD switch includes a powersplitter and an LCD array to block a non-desired path.
 7. The computersystem as defined in claim 1, wherein the photonic circuit switch is tochange the photonic connections less frequently than a rate of datapassing through the photonic circuit switch.
 8. The computer system asdefined in claim 1, wherein the allocated portion of the RAM isaddressable by the predetermined CPU selected from the plurality ofcomputer servers, and wherein a ratio of a maximum allocated portion ofthe RAM to CPU cores is at least 64 GB/core in the predetermined CPU. 9.The computer system as defined in claim 1, further comprising aconverter operatively disposed on the memory appliance between thephotonic circuit switch and the link-attached memory domains to convertphotonic CPU link signals to electronic CPU link signals.
 10. Thecomputer system as defined in claim 1, wherein the allocated portion ofthe RAM is exclusively addressable by the predetermined CPU selectedfrom the plurality of computer servers and wherein an allocation,established during the configuration event, of the portion of the RAMfor exclusive use of the predetermined CPU is maintained throughoutoperations of the computer system until a subsequent configurationevent.
 11. The computer system as defined in claim 1 wherein theconfiguration event includes an instantiation of a virtual machine. 12.A method for sharing computer memory in a computer system having aplurality of Central Processing Units (CPUs), the method comprising:photonically connecting the plurality of CPUs to a memory appliancespaced remotely from the plurality of CPUs, the memory applianceincluding link-attached memory domains having random access memory (RAM)therein; exclusively allocating via a photonic circuit switch a portionof the RAM, during a configuration event including a boot operation, toa predetermined CPU selected from the plurality of CPUs based on a sizeof a calculation task that the predetermined CPU is to execute;establishing and maintaining the exclusive allocation of the portion ofthe RAM to the predetermined CPU during operations of the computersystem until the configuration event; and controlling the photoniccircuit switch during the configuration event to change the photonicconnections between the plurality of computer servers and thelink-attached memory domains of the memory appliance.
 13. The method asdefined in claim 12 wherein a ratio of a maximum allocated portion ofthe RAM to CPU cores is at least 64 GB/core in the predetermined CPU.14. The method as defined in claim 12, wherein allocating the portion ofthe RAM to the predetermined CPU selected from the plurality of CPUsoccurs over a time duration of less than 100 milliseconds.
 15. Themethod as defined in claim 12, wherein a signal propagation time throughthe photonic circuit switch averages between 50 picoseconds and 500picoseconds.
 16. The method as defined in claim 12, further comprising:converting, by a converter operatively disposed on the memory appliancebetween the photonic circuit switch and the link-attached memorydomains, photonic CPU link signals to electronic CPU link signals. 17.The method as defined in claim 12, wherein the configuration eventincludes an instantiation of a virtual machine.
 18. A computer system,comprising: computer servers, each server including at least two centralprocessing units (CPUs), each CPU having at least two CPU coresoperatively disposed therein; a memory appliance including link-attachedmemory domains having a random access memory (RAM); a photonic CPU linkoperatively attached to each of the at least two CPUs; and a photoniccircuit switch operatively attached between the photonic CPU link andthe memory appliance to provide connections between the computer serversand the link-attached memory domains, wherein the photonic circuitswitch is controlled by an electronic control during a configurationevent to change the connections between the computer servers and thelink-attached memory domains of the memory appliance and to allocate aportion of the RAM, during the configuration event, to a predeterminedCPU in the computer servers based on database size that thepredetermined CPU is to search.
 19. The computer system as defined inclaim 18, further comprising a converter operatively disposed on thememory appliance between the photonic circuit switch and thelink-attached memory domains to convert photonic CPU link signals toelectronic CPU link signals.
 20. The computer system as defined in claim18, wherein the allocated portion of the RAM is exclusively addressableby the predetermined CPU during the configuration event, and wherein theallocation, during the configuration event, of the portion of the RAMfor exclusive use of the predetermined CPU is established and maintainedthroughout operations of the computer system until a subsequentconfiguration event.